Stainless steel metal-to-metal high speed seals



United States Patent 3,382,065 STAINLESS STEEL METAL-TO-METAL HIGH SPEED SEALS Theodore L. Oberle, Washington, and Glenn R. Gobble, Peoria, 111., assignors to Caterpillar Tractor Co., Peoria, Ill., a corporation of California No Drawing. Continuation of application Ser. No.

555,248, June 6, 1966. This application Oct. 6, 1967, Ser. No. 673,519

2 Claims. (Cl. 75-126) ABSTRACT OF THE DISCLOSURE A stainless steel metal-to-metal high speed seal is disclosed wherein the stainless steel consists of iron, chromium, carbon and boron. All costly exotic alloying elements such as columbium cobalt, molybdenum and vanadium are omitted. The stainless steel is extremely useful under severe service conditions as exemplified by the presence of highly corrosive and abrasive materials, such as mud and dirt. The stainless steel consists essentially of up to 3% carbon, .54% boron, from 15-35% chromium and the balance iron.

This application is a continuation of application Ser. No. 555,248, filed June 8, 1966, now abandoned, which in turn was a continuation-in-part of application Ser. No. 400,874, filed Oct. 1, 1964, and now abandoned.

The present invention relates to stainless steel and more particularly to a particularly wear and corrosion resistant stainless steel based upon iron and chromium and having alloying elements carbon and boron.

Stainless steels have found extensive application throughout industry because of their outstanding corrosion resistance under severe conditions. This property, coupled with wear resistance and other favorable metallurgical properties, has accounted for their increasing utilization. However, where such alloys have been sub jected to extremely severe service conditions, i.e., in the presence of highly corrosive and abrasive materials, such as mud and dirt, and wherein such alloys are used to form seals to protect vital machinery parts, it has been found necessary to resort to stainless steels having even more pronounced wear and corrosion resistance. In order to achieve such wear and corrosion resistance the industry has had to resort to alloy stainless steels including costly alloying elements such as columbium, cobalt, molybdenum and vanadium. Such alloys have been found to be highly suitable for such severe service use. However, it has been found desirable from both an economic standpoint and from a strategic availability standpoint to develop alloys suitable for such severe service use, but wherein such elements as vanadium, molybdenum, cobalt and columbium are unnecessary.

A stainless steel alloy has now been developed which is totally free from such exotic elements, but which, however, exhibits comparable properties of wear and corrosion resistance. Such alloy comprises a major amount of chromium, relatively minor amounts of carbon and boron, all alloyed within an iron base. Such stainless steel alloy differs from known stainless steel al'oys possessing similar corrosion and wear resistant characteristics in that the more exotic materials such as molybdenum, cobalt, vanadium and columbium are eliminated to achieve a corrosion resistant chromium-iron alloy with dispersed carbide and boride complexes. This resultant alloy is an extremely economical metallurgical composition which still exhibits the required characteristics for severe service use.

It is, therefore, an object of the present invention to ICE provide a stainless steel alloy having outstanding wear and corrosion resistant characteristics.

It is another object of the present invention to provide a stainless steel alloy from which all exotic materials such as molybdenum, vanadium, columbium and cobalt are eliminated.

It is still another object of the present invention to provide a stainless steel alloy utilizing the elements iron, chromium, carbon and boron.

It is still a further object of the present invention to provide a stainless steel alloy comprising a chromiumiron matrix with hard particles of carbide and boride complexes dispersed therein.

Yet another object of the present invention is to provide an alloy suitable for severe service conditions but comprising readily available and inexpensive alloying elements.

It is still another object of the invention to provide a stainless steel alloy having excellent wear and corrosion resistant characterisiics when utilized in metal-to-metal constructions involving both high and low speed relative motion between parts.

The alloy of the present invention comprises a material exhibiting the properties of a wear resistant, stainless steel wherein said properties are derived from a combination of the elements iron, chromium, carbon and boron. Iron is present in the alloy to the largest extent with somewhat lesser amounts of chromium and considerably smaller amounts of boron and carbon.

The useful range of the above noted elements in the alloy are as follows:

Percent Car'bon 0-3.0 Boron 0.5-4.0 Chromium 15-35 Iron Balance All of the above noted amounts weight.

The presence of chromium in the above stainless alloy imparts excellent corrosion resistance thereto. The lower range of chromium in the alloy is maintained high enough to secure at least an excess of 12% chromium in solid solution in the alloy. By maintaining at least 12% chromium in solid solution in the alloy, the proper stainless characteristics are maintained. On the other hand, if too great an amount of chromium is present in the alloy, an undesirable sigma phase is formed therein. The presence of such sigma phase in the alloy results in a high co-efiicient of thermal expansion which is undesirable when the alloy is used in various types of metal-to-metal seal constructions. Thus it has been found that if chromium is present in the alloy in excess of 40%, the nudesirable sigma phase is formed therein. Therefore, it is preferable to keep chromium within the range as specified above.

The element boron in the alloy serves to form intermetallic borides. These borides form extremely hard particles in the chromiunriron matrix material. Similarly carbon in the alloy serves to form intermetallic carbides having generally similar properties to the borides. These hard intermetallic borides and carbides dispersed throughout the solid solution of chromium-iron impart excellent wear resistant properties to the alloy. The excellent wear resistant property of the alloy is attributable to the greatly increased hardness imparted by adding increasing amounts of boron and carbon thereto. However it should be noted that the intermetallic compounds must be limited, since they induce extreme brittleness in the alloy when present in too great a quantity. The properties of the intermetallics, e.g., brittleness, are additive: and therefore increasing the total amount of boron and carbon in the are in percentages by alloy to amounts greater than indicated results in an alloy generally too brittle for any extensive usefulness thereof. Generally speaking, Where the alloy of the invention is to be used in applications such as bushings for metal-tometal seals the total content of boron plus carbon in the alloy should not exceed 7% by weight. Increased aggregations of boron and carbon result in an alloy too brittle for such use. It should be noted that while the relative amount of boron and carbon may be varied within the ranges of individual elements set forth, it is only the total aggregate amount of boron and carbon which is limited to 7% The lower limits of carbon and boron are set to provide sufii- 4 1 a The following chart identified as Example 1, indicates a comparison of several different castings of the present alloy with castings of several previously known alloys. These castings were of metal-to-metal ring seals having compositions as noted in the chart. The samples indicated C-6 and C7 are both alloys presently utilized for commercial ring seals. All of the castings were fabricated in standard ring seal units and then subjected to a running test for 1000 hours in a mud bath. The castings were then inspected and measured for wear. Such a test yields data indicating the wear resistance of the seals and their indicated suitability for severe corrosion and wear conditions.

EXAMPLE I Alloy Analysis in Percent by Weight Re Wear,

Sample Hardness inches/ B Mo V 00 Cr Fe 1,000 yrs.

4. 66 25. 0 Del. 61-63 0. 00017 4 40 25. 0 130.1. 66-68 0.00617 3 35 25.0 Bal. 63-65 0.00035 3 32 25. 0 Bal. 62-67 0. 00031 2 20. 0 Bal. 65-68 0.00012 2 50 25. 0 Bal. 08-70 0. 00025 8. 60 25. 0 Ba]. 71 0. 00009 17. 0 Bal. 66-67 0. 0002 cient intermetallic compounds to induce good wear resistance in the alloy, since as noted above, the intermetallic compounds account for the hardest components of the alloy. While alloys of the present invention become quite brittle when the aggregate of carbon and boron approach the upper limit of 7%, investigations have shown that such alloys are extremely useful in high speed metal-tometal constructions such as seals. Despite their brittleness, such high carbon-boron alloys exhibit greatly superior wear characteristics over conventional stainless alloys especially in high-speed applications. In addition, when utilized in properly designed seal constructions, the brittleness does not impair or limit the seal life.

Iron is of course the predominant element in the alloy and in the presence of the amounts of chromium as indicated above, forms a solid solution therewith having excellent corrosion and stain resistant properties.

The alloys of the invention can be produced by metallurgical alloying techniques commonly practiced in the art. The alloy also furnishes an excellent material for the production of cast products wherein extreme hardness and outstanding stain resistance are desirable. For instance, the alloy of the invention was cast into metal-tometal ring seals which after a heat treatment at between 1950 and 2000" F., cooling in air, a subsequent heat tempering to 900 F. for one hour, and subsequent cooling in air produced ring castings having a Rockwell C hardness of 61-74. In addition such ring seal castings under test conditions exhibited wear rates comparable with stainless steel alloys containing large amounts of exotic alloying materials such as molybdenum, cobalt and vanadium.

From the chart above it can be seen that alloys of the present invention have wear resistant properties comparable to or better than commercially used alloys. And in addition the present alloys are less expensive to produce since such exotic elements as vanadium, molybdenum, and cobalt are not present.

What is claimed is:

1. Stainless steel metal-to-metal high speed seals having improved wear resistance, said stainless steel consisting essentially of up to 3% carbon, 0.54% boron, from 15 to about 35% chromium and the balance iron.

2. The stainless steel metalto-metal high speed seals according to claim 1 wherein said steel consists essentially of about .30 up to about 2.60% carbon; about 2.25 up to about 4.66% boron; about 20 up to about 25% chromium; balance iron.

References Cited UNITED STATES PATENTS 1,493,191 5/1924 De Goyler 75126 1,671,417 5/1928 Franks 75126 1,493,191 5/1924 De Golyer 75-12 6 2,311,878 2/1943 Schlumpf 75126 3,334,996 8/1967 Foster 75126 3,340,047 9/1967 Persson 75-126 CHARLES N. LOVELL, Primary Examiner.

DAVID L. RECK, HYLAND BIZOT, Examiners.

PAUL WEINSTEIN, Assistant Examiner. 

